####018002251#### FXUS01 KWBC 171821 PMDSPD Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 220 PM EDT Wed Apr 17 2024 Valid 00Z Thu Apr 18 2024 - 00Z Sat Apr 20 2024 ...Severe weather and isolated flash flooding for the Great Lakes/Ohio Valley this evening; threat shifts to the Ohio and middle Mississippi valleys and Southern Plains Thursday... ...Warm to hot temperatures across the southern U.S.; chillier weather spreading southeast from the northern Rockies/Plains... Showers and thunderstorms will continue to develop into the evening along and ahead of a cold front now advancing eastward across Lower Michigan and the Ohio Valley. Some of these storms may become strong to severe, producing damaging winds, large hail, and a few tornadoes. In addition to severe weather, locally heavy rainfall and isolated flash flooding are concerns as well. Later this evening, storms are forecast to develop from the central Plains into the lower Missouri Valley. These storms too may become strong to severe, with damaging hail expected to be the primary threat. As the system in Plains moves further east, storms are likely to redevelop from the Ohio Valley into the southern Plains on Thursday. Severe weather will once again become a concern, especially across portions of the mid Mississippi into the lower Ohio valleys. The Storm Prediction Center has issued an Enhanced Risk (level 3/5) for portions of the region, noting that strong to severe storms capable of damaging winds, and possibly a few tornadoes, are likely tomorrow. While widespread heavy rains are not expected, locally heavy accumulations resulting in isolated flash flooding are possible. Temperatures across the southern U.S. will remain warm through the period, with highs in the upper 80s and 90s common from the Southwest to the Southeast over the next couple of days. Much cooler temperatures now centered over the northern Rockies and Plains will spread southeastward, lowering temperatures across much of the Midwest and Ohio Valley by Friday. Pereira Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php $$ ####018004629#### FXUS02 KWBC 171822 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 222 PM EDT Wed Apr 17 2024 Valid 12Z Sat Apr 20 2024 - 12Z Wed Apr 24 2024 ...Overview... The pattern during the medium range period will continue to transition to more progressive flow by this weekend as an Omega block over the northeast Pacific into western North America and the northern U.S. tier begins to break down. Energy from the west side of a deep upper low initially over southeast Canada on Saturday will interact with another shortwave into the Southern Plains, increasing the heavy rain threat on Saturday especially across much of Texas, then continuing to a lesser extent into Sunday across the Southeast. Secondary energy ejecting from an upper low/trough over the Northeast Pacific will skirt the northern tier and move through the Great Lakes into the Northeast early next week. Troughing generally will get reestablished over the West Coast by next Tuesday-Wednesday. ...Guidance/Predictability Assessment... The latest guidance shows very good agreement across the CONUS through much of the period (Saturday-Wednesday). There are some timing differences with shortwave troughing through the Southeast Sunday-Monday and again with the next shortwave through the Great Lakes/Northeast Tuesday-Wednesday. These details create some uncertainty in the eventually (generally light) precipitation pattern across the Southeast and Northeast early next week. Generally favored the model/ensemble consensus for now. There is more uncertainty late period with the evolution of a deep closed low over the Gulf of Alaska which may split into two factions -- the southern part likely headed towards the West Coast by next Wed. The GFS/GEFS were quicker than the ECMWF/ECMWF ensembles (which had support from the AIFS-ECMWF). Favored a middle-ground to slower solution than a straight consensus. The WPC forecast used a blend of the 06Z GFS/GEFS and 00Z ECMWF/CMC this morning with more weight toward the ECMWF by the end of the forecast period. ...Weather/Hazards Highlights... Shortwave energy into the Southern Plains interacting with a slow- moving frontal boundary and anomalous moisture/instability will increase the threat for heavy to excessive rainfall across much of the Southern Plains into the Lower Mississippi Valley on Saturday. A Slight risk continues on the Day 4 Excessive Rainfall Outlook (Sat-Sun morning) across central to northeast Texas. Rainfall will continue into the Southeast/Carolinas on Sunday as the front slowly sinks through that region, though amounts overall look to be lower than on Day 4. This is depicted as a Marginal risk on the Day 5 ERO. The next shortwave through the Northern Plains-Great Lakes- Northeast will be accompanied by some generally light rain early next week. The upper trough over the northern tier states and eventually into the East will support below normal temperatures (with greater anomalies for highs than lows) for most areas east of the Rockies except Florida by next weekend. Above normal temperatures across the Southwest should gradually expand northward underneath a building Western U.S. ridge and progress eastward into the Rockies early next week. Northern parts of the West may stay near normal due to the upper shortwave/cold front crossing the region next week. Fracasso/Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$